Soil water repellency (SWR) is a condition where soil does not spontaneously wet when a drop of water is applied to the surface; in other words, the soil is too hydrophobic (Müller and Deurer, 2011). Hydrophobic soils occur in many countries on various lands, such as agricultural, pasture, coastal dune sands, forest, shrub lands, parks, turfgrass soils, no-till agriculture, and soils irrigated with treated wastewater. A substantial interest in SWR soils has grown in recent times (Blanco-Canqui, 2011; Dekker et al., 2005).
SWR can cause undesirable consequences such as environmental deterioration and considerable losses in crop production. SWR becomes especially problematic on water relationships and can cause associated environmental issues, such as, but not limited to, reduction in soil water intake, uneven wetting patterns, reduced irrigation efficiency and effective precipitation, increased preferential flow that can have adverse effects on aquifer contamination, greater runoff and erosion, limited seed and vegetative establishment, and reduced plant growth and quality (Doerr et al., 2000; Müller and Deurer, 2011). On sandy turfgrass soils and grasslands, SWR is a reoccurring problem, where the normal situation is called “localized dry spot” (LDS). In LDS, SWR appears as irregular dry areas from a few centimeters to several meters diameter with the repellency usually extending from the surface to 5-10 cm depth. A second SWR situation on turfgrass sites that can appear on all soil types occurs within the dry area of basidiomycete induced “fairy-ring” (Barton and Colmer, 2011; Fidanza et al., 2007).
The primary cause of SWR is formation of a coating of hydrophobic, organic material on soil particles. This hydrophobic organic material can include surface waxes, fatty acids, and other organics such as lignin, a recalcitrant polymer of phenols. These materials come from plant leaves and other decomposing organic matter, plant root exudates, fungal hyphae/exudates, and volatized organic materials condensing on soil particles following forest or grassland fires (Atanassova, 2010). Sandy soils are especially susceptible to SWR due to lower particle surface area. Once sands become coated by organics and upon drying to a critical moisture level, they exhibit a hydrophobic nature and, thereafter, resist rewetting. The conventional remediation practice involves the use of wetting agents (surfactants); but, this indirect approach is costly and only renders short-term positive effectiveness, with repeated applications needed to maintain hydrophilic conditions (Müller and Deurer, 2011; Moore et al., 2010). For recreational turfgrass sites with SWR, wetting agents are applied as a routine practice in the absence of other effective remediation practices. Biological methods have been attempted, involving culturing microorganisms capable of degrading wax in soil, and have shown to be effective at the lab scale (Müller and Deurer, 2011). However, considerable limitations still exist in practical field application in terms of costs and maintenance of inoculation population levels (Roper, 2006).